1. Field of the Invention
The present invention relates to a computer system, and more particularly to a controlling system for a VGA module built in the motherboard where an add-on video card can be received in an expansion slot.
2. Background Art
The video card or video adapter provided with personal computers functions as a hardware interface with a display device. An exemplary computer system comprises a central processing unit (CPU), a BIOS, a main memory, an interface controller with an auxiliary storage, and a video adapter, which are linked to a system bus. The video adapter deals with image data and outputs the video signal to a display device such as cathode ray tube (CRT) or liquid crystal display (LCD). Sometimes, the video adapter is incorporated into a motherboard by PC manufacturers to lower the overall cost as well as to improve reliability of the computer system. Also, added are expansion slots to enable new features and enhancements to be added to the system as well as allowing the quick and easy alteration of certain computer prerequisites, such as video adapters. When an add-on video card is used in such a motherboard design, the built in or internal video adapter module should be disabled. Disabling of the internal video module is performed by a jumper setting method which connects or disconnects a device identification signal line provided between the video adapter and the system bus such as a PCI bus. Initially, the jumper is set to the connected state to notify the computer system of presence of the internal module, thereby enabling the internal video module. If an add-on video card is used, the jumper is set to the disconnected state manually before or after the add-on video card is inserted in one of the expansion slots. This disables the internal adapter module and enables the add-on video card after an initialization procedure. The manual jumper setting process for enabling or disabling the built in video module is troublesome and this design is not in agreement with the plug and play requirements of some operating systems and corresponding hardware design guide.
U.S. Pat. No. 5,374,940 to Mark A. Corio entitled System For Operating A Plurality Of Graphics Displays From A Single Computer contemplates utilizing a plurality of video graphic cards connected to respective ISA expansion slots of a computer's motherboard wherein each video graphic card is addressable and provides data for display to a respective display monitor. The foregoing patent, however, does not contemplate usage within a PC where there is a video adaptor forming an integral part of the motherboard.